1. Field of the Invention
The present invention generally relates to a method and apparatus for data compression and decompression, and more particularly to a method and apparatus for compression and decompression which improves operation speed by employing parallel signal processing in an efficient manner.
2. Discussion of the Background
A variety of data compression apparatuses have been developed for use in the computer area. As an example, FIG. 24 shows a typical wavelet conversion apparatus which includes a wavelet converter 800 and an encoder 801. The wavelet converter 800 is configured to perform a two-layered wavelet conversion, and includes analytic subband filter banks 802-807. Each of the filter banks 802-807 includes a low pass filter (LPF) and a high pass filter (HPF) and two two-times downsamplers, indicated by ↓2 in FIG. 24.
In FIG. 24, an input image signal is horizontally subband-analyzed by the filter bank 802 and the resultant low and high pass coefficients are vertically subband-analyzed by the filter banks 804 and 803, respectively. The analysis made by the filter banks 802-804 is referred to as the first layer analysis. Then, the low pass coefficient output from the filter bank 804 is horizontally subband-analyzed by the filter bank 805 and the resultant low and high pass coefficients are vertically subband-analyzed by the filter banks 807 and 806, respectively. In this way, the wavelet converter 800 outputs wavelet conversion coefficients 1LH, 1HL, 1HH, 2LL, 2LH, 2HL, and 2HH in the seven subbands analyzed, as shown in FIG. 25. These wavelet conversion coefficients are input to the encoder 801, and the encoder 801 outputs a coded signal.
FIG. 26 shows a typical wavelet reverse conversion apparatus for reconstructing an original image by performing a reverse conversion based on an input coded signal. The input coded signal is generated in the above-mentioned way, for example. This wavelet reverse conversion apparatus of FIG. 26 includes a decoder 851 and a wavelet reverse converter 850. The decoder 851 decodes the input coded signal and outputs two-layered wavelet conversion coefficients 1LH, 1HL, 1HH, 2LL, 2LH, 2HL, and 2HH. The wavelet reverse converter 850 is configured to perform a two-layer reverse wavelet conversion, and includes synthetic subband filter banks 852-857. Each of the filter banks 852-857 includes a low pass filter (LPF) and a high pass filter (HPF) and two two-times upsamplers, indicated by ↑2 in FIG. 26.
The output two-layered wavelet conversion coefficients 2LL, 2LH, 2HL, and 2HH are vertically subband-synthesized by the filter banks 857 and 856, and the resultant synthesized coefficients are horizontally subband-synthesized by the filter bank 855. Then, the coefficient output from the filter bank 855 and the coefficient 1LH are vertically subband-synthesized by the filter bank 854, and the coefficients 1HL and 1HH are vertically subband-synthesized by the filter banks 853. After that, the coefficients output from the filter banks 854 and 853 are horizontally subband-synthesized by the filter bank 852 and the resultant output from the filter bank 852 is, accordingly, the original image signal. In this way, the wavelet reverse converter 850 outputs the original image signal.
The technology of the above-described data compression apparatus is described in “Introduction to Wavelet,” C. K. Chui, Academic Press, New York, 1992. Also, the above-mentioned type of data compression apparatus is described in U.S. Pat. No. 5,748,786, issued May 5, 1998 to Ahmad-Zandi, et al.